Mass Effect - Q&A @ Official Blog

How many people can be in a "squad"? Is it three like in the videos?Yep - three. It’s like in “Star Wars: Knights of the Old Republic,” where you pick the other two squad mates from a larger group of six. We’re sometimes asked, “Why three?” The answer is that from a game design standpoint (and in lots of other design applications actually); three is kind of a “sweet spot” number. Three is the lowest number where you get certain benefits that result from the concept of a group. When there are only two characters, any interaction with your squad (combat movements, conversations, etc.) must involve yourself and the other person. But with three, there can be an interaction that involves part of the group but not the other, and therefore the concept of “choice” becomes possible. And though there’s a big difference in the group dynamic between two and three, not much new happens with four or more.

So having a squad of three means we have a group that’s small and manageable, but also supports interesting choices and situations. For example, your squad members comment on places you explore and decisions you make. But since there are two other characters, they’ll actually have conversations between themselves. It also means that in combat, you have lots of choices in terms of whose special abilities you’ll use, where you’ll position your squad members as you breach a doorway, or who will stay behind and who will move ahead to spot enemies.